1. Field of the Invention
The present invention relates to the switching of a load connected by a bidirectional switch to an A.C. network or by a one-way switch to an A.C. network rectified by a rectifying bridge. The present invention for example finds applications in the control of medium-power loads, for example, a vacuum cleaner motor, a temperature-controlled heating circuit, a dimmer lighting system, etc.
2. Discussion of the Related Art
FIG. 1 very schematically shows such a switching circuit. Load 1 is arranged between terminals A and B of an A.C. voltage or of a rectified A.C. voltage, in series with a power switch SW. Switch SW will be called a power switch, although it is, in the given examples, a medium-power switch intended for switching loads connected to the mains. Switch SW is controlled by a control circuit 2 receiving a control order, periodic or not, on a terminal 3. The control circuit is, for example, intended for turning on the switch for a portion only of a halfwave of the A.C. voltage across terminals A and B, which corresponds to a so-called phase angle control. Then, when the switch turns on, a strong current surge occurs in the load. In other words, the current variation along time (di/dt) is abrupt and the current exhibits strong peaks upon each turning-on of the switch.
These current peaks are capable of being sent back by terminals A and B onto the A.C. supply network and to disturb this network and other circuits connected to this network.
Conventionally, to attenuate these disturbances, an inductance L of relatively high value is provided in series with the switching circuit, which, independently from the cost of this inductance, which is a discrete component of relatively large dimension, complicates the circuit design.
U.S. Pat. No. 6,127,746 discloses a relatively complex circuit for detecting current peaks and controlling a MOS transistor so as to dampen these current peaks.
Japanese patent application 07/131316 provides for detecting overcurrents on an output pad of a MOS transistor by surrounding this pad with a winding, whereby the surface area of the semiconductor chip containing the transistor is substantially increased.